1. Field of the Invention
The present invention relates to a plasma display panel and, more particularly, to a plasma display panel that can reduce an appearance of a stain around an exhaust aperture and an exhaust tube.
2. Description of the Related Art
Generally, a plasma display panel (PDP) is a display device that can display an image using red, green and blue visible light created by exciting phosphors using vacuum ultraviolet (VUV) rays emitted from plasma generated by a gas discharge. In an alternating current (AC) plasma display panel, address electrodes are formed on a rear substrate. The address electrodes are covered with a dielectric layer. Barrier ribs are arranged in a striped pattern on the dielectric layer between the address electrodes. Red, green and blue phosphor layers are formed on the barrier ribs. A plurality of display electrodes, each having a sustain electrode and a scan electrodes, are arranged on an inner surface of a front surface. The display electrodes extend in a direction intersecting the address electrodes. The display electrodes are covered with a dielectric layer and a MgO passivation layer. Discharge cells are formed at regions where the address electrodes formed on the rear substrate intersects the sustain and scan electrodes formed on the front substrate. Typically, millions of the discharge cells are arranged in a matrix pattern in the plasma display panel.
A memory property is used for driving the discharge cells of the plasma display panel. Describing in more detail, in order to generate a discharge between the sustain and scan electrodes, a potential difference higher than a threshold voltage is required. This threshold voltage is called a firing voltage (Vf). When scan and address voltages are respectively applied to the scan and address electrodes, a discharge is generated between the scan and address electrodes to create plasma in the discharge cell. Electrons and ions of the plasma travel to electrodes having polarities opposite to that of the electrons and ions.
Meanwhile, a dielectric layer is deposited on each electrode of the plasma display panel so that space charges can accumulated on the dielectric layer having an opposite polarity. As a result, since net space potential between the scan and address electrodes becomes lower than an initially applied address voltage (Va), the address discharge is weakened and disappears. At this point, a relatively small amount of electrons accumulates on the sustain electrodes and a relatively large amount of electrons accumulate on the scan electrodes. The charges accumulated on the dielectric layer covering the sustain and scan electrodes during the address discharge are called wall charges (Qw). A space voltage generated between the sustain and scan electrodes by the wall charges is called a wall voltage (Vw).
In a case where a discharge sustain voltage (Vs) is applied to the sustain and scan electrodes, when a sum (Vs+Vw) of the discharge sustain voltage (Vs) and the wall voltage (Vw) becomes higher than the firing voltage (Vf), a sustain discharge occurs in the discharge cells, thereby generating vacuum ultraviolet rays. The vacuum ultraviolet rays excite the corresponding phosphor layer to emit visible light through the transparent front panel.
However, when there is no address discharge between the scan and address electrodes (i.e., when no address voltage (Va) is applied), the wall charges do not accumulate between the sustain and scan electrodes. As a result, no wall voltage exist between the sustain and scan electrodes. At this point, only the discharge sustain voltage (Vs) applied between the sustain and scan electrodes. Since the discharge sustain voltage is lower than the firing voltage (Vf), the gas space defined between the sustain and scan electrodes cannot be discharged. In this way, only cells selected during the address discharge will produce a plasma during the sustain discharge.
The plasma display panel further includes an exhaust aperture and an exhaust tube that are provided at a portion of the rear substrate. The exhaust aperture and tube provide a passage through which an interior defined between front and rear substrates that are sealed together can be exhausted, after which discharge gas is injected. After the discharge gas is injected, an end of the exhaust tube is sealed to provide a sealing structure for the plasma display panel.
The exhaust tube is attached to the rear substrate by frit. That is, the melted frit is applied around the exhaust aperture of the rear substrate and the exhaust tube is attached to the melted frit. When the frit is cooled and solidified, the exhaust tube is securely attached around the exhaust aperture. When the exhaust tube is attached to the melted frit as described above, a portion of the frit is located inside of the exhaust tube and the rest of the frit is located outside of the exhaust tube.
The frit generates impurity gas as it is phase-changed from the high temperature melted state to the low temperature solid state. At this point, the impurity gas generated from the frit adjacent to a display area is absorbed in the display area. When the plasma display panel is driven, the absorbed impurity gas generates a stain around the exhaust aperture and the exhaust tube, thereby deteriorating the quality of the plasma display panel. Therefore, what is needed is an improved design for a plasma display panel that leads to a smaller sized stain in the display area.